Enantiomerically Pure Phosphaalkene–Oxazolines (PhAk‐Ox): Synthesis, Scope and Copolymerization with Styrene

The design of a synthetic route to a class of enantiomerically pure phosphaalkene–oxazolines (PhAk‐Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha‐Peterson reaction) was used as the PC bond‐forming step. Attempted condensation of PhC(O)Ox (Ox= CNOCH( i Pr)C H 2 ) and MesP(SiMe 3 )Li gave the unusual heterocycle (MesP) 2 C(Ph)CN‐( S )‐CH( i Pr)CH 2 O ( 3 ). However, PhAk‐Ox ( S , E )‐MesPC(Ph)CMe 2 Ox ( 1 a ) was successfully prepared by treating MesP(SiMe 3 )Li with PhC(O)CMe 2 Ox (52 %). To demonstrate the modularity and tunability of the phospha‐Peterson synthesis several other phosphaalkene–oxazolines were prepared in an analogous manner to 1 a : TripPC(Ph)CMe 2 Ox ( 1 b ; Trip=2,4,6‐triisopropylphenyl), 2‐ i PrC 6 H 4 PC(Ph)CMe 2 Ox ( 1 c ), 2‐ t BuC 6 H 4 PC(Ph)CMe 2 Ox ( 1 d ), MesPC(4‐MeOC 6 H 4 )CMe 2 Ox ( 1 e ), MesPC(Ph)C(CH 2 ) 4 Ox ( 1 f ), and MesPC(3,5‐(CF 3 ) 2 C 6 H 3 )C(CH 2 ) 4 Ox ( 1 g ). To evaluate the PhAk‐Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1 a and styrene were subjected to radical‐initiated copolymerization conditions to afford [{MesPC(Ph)(CMe 2 Ox)} x {CH 2 CHPh} y ] n ( 9 a : x =0.13 n , y =0.87 n ; GPC: M w =7400 g mol −1 , PDI=1.15).